In response to the demand for more reliable and higher capacity data storage and retrieval systems, there is considerable activity in the research and development of so-called optical disk recording systems. These systems utilize a highly focused modulated beam of light, such as a laser beam, which is directed onto a recording layer which is capable of absorbing a substantial amount of light. The heat thus produced causes the light-absorbing material in the areas struck by the highly focused laser beam to change chemically and/or physically, thus producing a concomitant change in optical properties, e.g. transmissivity or reflectivity in the affected area. For readout, the contrast between the amount of light transmitted or reflected from the unaffected parts of the absorbing layer and from the marked areas of the layer is measured. Examples of such recording systems are disclosed in numerous patents such as U.S. Pat. Nos. 3,314,073 and 3,474,457. In recording data, a rotating disk having a light-absorptive recording layer is exposed to modulated radiation from a laser source. This radiation is passed through a modulator and appropriate optics and the highly focused laser beam is directed onto the disk which forms by chemical and/or physical reaction of the light-absorbing layer a series of very small marks along a circular path within the light-absorptive layer. The frequency of the marks is determined by the modulator inputs. Using laser beams with a diameter of 1 micron or less, data can be stored at a density of 10.sup.8 bits/cm.sup.2 or higher.
The simplest optical disk medium consists merely of a dimensionally stable solid substrate on which is coated a thin layer of light-absorptive material such as a metal layer. When the light-absorptive layer is struck by an intense beam of coherent light, such as from a laser source, the light-absorptive material is vaporized, thermally degraded, and/or otherwise physically and chemically modified, thereby producing a very small marked area which exhibits different transmissivity or reflectivity than the adjacent unmarked layer.
The desired properties of optical recording media are (1) high sensitivity, (2) high signal-to-noise ratio (SNR), (3) high tolerance to material variation, contaminants and other defects, and (4) high archival stability after extended storage and/or recording and readout (see Bartolini J. Vac. Sci. Technology Vol. 18, No. 1. Jan/Feb. 1981, P.70).
A wide range of materials have been used as the light-absorptive material for the recording layer of optical recording elements. For example, thin films of metals, particularly tellurium and its alloys have been used. A number of organic based light-absorptive materials have also been employed, particularly dye/polymer composites in which an organic dye is dissolved or dispersed in an organic polymer binder. Examples of dye-containing recording media are disclosed in U.S. Pat. Nos. 4,023,185, 4,097,895, 4,101,907, 4,190,843, 4,218,689, 4,219,826, 4,241,355, 4,242,689, 4,315,269 and WIPO Patent Publication Nos. WO84/02794 and WO84/02795.
More recently the use of polymeric dyes as optical recording media has been disclosed. Examples of such media are disclosed in U.S. Pat. No. 4,501,876 and Japanese Kokai Nos. JA59-045195, JA59-062188, JA59-185694, JA59-229396, JA59-232894, JA59-232896, JA60-018387 and JA60-044554.
Despite the great amount of research and development in this area of technology and the great number of materials tested, there is still a demand for a material which will exhibit the capability of being formed into optically suitable imaging layers with both low cost of manufacture and with high performance reliability and stability.